The Testo 557 Evaluation
One of the little touted features of the very first generation 523 was absolute pressure sensors which offered extremely high accuracy at all elevations compared to the relative pressure sensors used by the rest of the industry. (Again, Testo was simply ahead of their time.) The downfall of this, aside from the higher cost, was the fact that the instrument required a dead-band of about +/- 3 psi to hide changes in barometric pressure when used in the PSIG mode, (gauge pressure versus absolute) making them unusable for some refrigeration applications that operated close to 0 or in a slight vacuum. (This confused and still confuses many technicians.)
The 557 uses a vacuum rated manifold that has been helium tested for leakage. Utilizing 4 ports allows for the connection of the vacuum pump (3/8") and refrigerant tank (1/4") at the same time minimizing the possibility of exposing the system to atmosphere when commissioning a system. The use of vacuum rated hoses is strongly recommended for this type of system as standard hoses are not adequate or rated for evacuation.
Static build up is a potential problem with all digital and analog refrigeration gauges. When refrigerant (a very good dielectric) is passed through a hose a static charge can be generated. If not dissipated it can be a source of temperature measurement errors, pressure errors, an uncomfortable shock for the user, and/or damage to the meter or sensors. The Testo 557 and 550* use grounded temperature probes eliminating the need of a grounding strap when charging or recovering refrigerant. Static charges are bled off instead of building in the instrument eliminating errors, annoying static shocks and/or damage to the instrument.
When you examine the 557, you will notice a few changes in construction, especially if you have an early model 550. The hook used on the 557 and the newer 550's has been significantly improved in strength. The new hook base is a much larger diameter which will eliminate hook failures. The battery door is sealed with an o-ring to provide additional resistance to moisture and dirt. The display (still a backlit LCD) now has a Plexiglas shield to protect against breakage.
The testo 557 measures vacuum with a barometric pressure compensated relative pressure sensor. The sensor is limited as it has a 500 micron resolution, but it does provide an adequate indication of vacuum for most users. When evacuating a system after our testing, we recommend that the pump is operated until the 557 display reaches a level of 000 microns indicating it is somewhere below 500. The 557 does not have the accuracy or the resolution for a standing pressure test (to indicate leakage) in a vacuum, but it does have a temperature compensated pressure test for this purpose. For all refrigerants especially those utilizing POE oils like R410a, a standing test in a vacuum is not recommended as a means of testing for system tightness as any leaks will introduce moisture into the system thereby contaminating the refrigerant oil and possibly damaging the system. After evacuation is complete, the 4 valve manifold allows for the isolation of the vacuum sensor from the vacuum pump. After a short stabilization period, it is easy to determine if the level of vacuum is adequate. We recommend the use of vacuum rated hoses and core removal tools with the 557 to minimize the potential leaks.
Two temperature inputs allow simultaneous calculation and display of superheat and subcooling. With just a press of a button, the differential temperatures are also displayed. With another press of a button, you can quickly switch between the different measurements. The testo 557 features a large, backlit LCD display. Large numbers help you quickly and easily read the values. Intuitive operation provides you the ability to quickly analyze and diagnose the system without changing connections or performing tedious calculations. In a few seconds the instrument displays all of the values you need for an accurate and precise analysis.
The testo 557 incorporates a compact design for ease of use, transport and set up. The testo 557 has a durable housing that protects the analyzer from the everyday bumps and drops. It is built for the field. The testo 557 is a full function analyzer. With 39 refrigerant profiles plus H2Ostored on the processor and unique temperature and atmospheric pressure compensated sensors, the testo 557 is one of the most accurate analyzers on the market. Say goodbye to the old fashioned PT charts and temperature probes!
With a testo 557 Refrigeration System Analyzer, multiple tests are performed and calculated all at once. Just select the results you want displayed and away you go! Once connected, you can perform a leak test, system evacuation, and monitor charging. Refrigerant flow can be monitored in the integrated (magnified) sight glass. Superheat and subcooling can be measured and displayed in real time!
Pros:
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Atmospheric compensation of the relative pressure sensors. (This feature alone justifies the purchase.)
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Overall much better construction than the first release of the 550. Testo paid attention to the details
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No grounding strap required (One less step.)
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Hook issue has been addressed
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3/8" vacuum port allows for faster evacuation and recovery
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Temperature compensated tightness test is very useful. This can help minimize moisture contamination in 410a systems.
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Thermistors that do not require field calibration and hold calibration much more accurately over time
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Super easy to use
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Not a big fan of vacuum in the manifold. Hoses tend to leak! Use vacuum rated hoses (TruTech Tools has them) if you plan to use the vacuum feature of the instrument. The good news is that the sensor cannot be contaminated!
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Vacuum resolution. I would have like to see a resolution of at least 100 microns. (What can I say we are purists! We like to see vacuum in 10ths of a micron.)
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New temperature probes do not eliminate the grounding strap for the early 550s. First generation 550's will always require the grounding strap as there are hardware changes in both the meter and the probe.
13 Comments
peter savage
i do not understand temperature compensation test. in minimizing moisture in r410a system
Jim Bergmann
Using pressure to verify a leak versus using a vacuum has several advantages including higher test pressures and the fact that moisture will not get pulled into a pressurized system. The temperature compensated pressure test is far more accurate than a traditional pressure drop test and assures that when performing an evacuation no moisture gets pulled into the system. Since moisture and POE oil are not friends, this is how the system is better protected.
brian
So what's the point of putting a vacuum pump on it if it doesn't know or go up on the display . and you have to pressurize with nitrogen to see if there's a leak. or am I confused
Jim Bergmann
The 557 an 570 display vacuum and read in microns. The reason we want to test under pressure is vacuum is limited to -14.7 psi. We can easily test at 10 times (150 psi) that pressure with nitrogen. The instrument can also determine if the system is leaking or not by measuring both pressure and temp and using the gas laws to determine tightness. You cannot do that in a vacuum. Also if we do have a leak, we do not want to pull moisture into the system in a vacuum.
john
Just a comment; I am still out on the Testo 557. However, I do wonder about your 100 micron comment. Some oils tend to vaporize at lower micron settings. After being in this for 30 years I find I know so much less than I need. I feel there is some confusion on how low to actually pull a closed system with a compressor attached. Also, a true dry system is considered at 1000 microns steady of course/correct or no??. I usually go to 500. Is this old guy behind on this one and thanks for these in
Reuben
That question intrigues me too. Compared to Fieldpiece, how strong has the manifold been? I have been through 3 sets of valve stem nylon caps on the SMAN-3, always seeming to come out of the stem in the middle of vac or charge on massive flooded condenser systems. Twice, I have had to break vac on a system to pull my manifold apart and dig out the nylon caps. No bueno.
Art kellerman
Note that you have to be careful using the temp clamp on probes if they snap closed they can break due to the strength of the spring. I had this happen to me and had to by a new probe. Art Kellerman.
Robert Young
Hello.... Im still not sure which one I want 550 or the 557 I'm leaning towards the 550 with the blue vac vacuum gauge. If you think the 557 would be better as I do mostly residential Hvac I would appreciate your input.... Thank You.
David Fernandez
Very nice piece of equipment I would like to get one in the future....
Raymond Wilkie
GREAT TOOL [ USE THE 570 & 550 ON 60 TON FREEZERS DATA LOG [S AWSOME FOR RECORDS THX RAY
Raul Rodriguez
To whom it may concern i bought my testo 550 wich i like better the the other brands out there dut already had to send them out for repair when i recived them i was happy but that came back with the same issues ican not be sending them back to get checkt out the report that thay send back was thaat every thing was fine it seems thay got there and ssent back not a happy custermor i work in florida so wrod of mouth is harsh
Ding pong
Hi I just got my Testo 557, but I am really confused how the vacuum works on this maninold gauge, I attached the vacuum sensor in between the yellow hose with a T union joint and pressed the mode button to vacuum mode, however, there is only 0000 shown in the top left corner but the value doesn't change at all and the micron word never shows up, it that something wrong?
Stuart Smith
I have the older style of hook on my gauges. Any chance I can get a replacement? I can't seem to find a part number or availability on your site. I use these way too much to send them in just to replace a hook.
Rene
I am getting my second pair of test 557 and I am waiting to see how this pair works out. I know my previous one was not the best and had issues with the sensor. So lets see!